1. Field of the Invention
This invention relates to non-invasive, ultrasonic imaging systems, especially high resolution, well-focused systems for obtaining images of internal organs of human or animal bodies.
2. Prior Art
In the field of ultrasonic imaging, there are a number of desiderata, such as: high resolution, proper focus, short data-gathering time, low susceptibility to motion of the body being examined, good signal-to-noise ratio, and simplicity and inexpensiveness of the associated electronics.
Conventional ultrasonic imaging systems included those in which the entire aperture is used simultaneously to form the energy-transmitting beam and to receive returning echo signals. If a phased array is employed in producing the beam, electronic circuits such as delay circuits are required for each element of the array. Moreover, because the entire aperture is used, there will be a limited depth of field and steps must be taken to achieve dynamic focus during reception of the reflected signals. Nevertheless, since each pixel of the scene is interrogated by insonification only once in deriving the signals used in forming the image, this type of system is relatively immune to motion of the object during scanning.
Another approach, known as the "synthetic aperture" system employs only part of the available aperture at any given time. Therefore, no transmit beam is formed which needs to be focused and simpler electronic hardware can be used. One such system is disclosed in the co-pending application, Ser. No. 520,573 of Luthra, Kassam and Bernardi entitled "Body Imaging Using Signal Processing to Achieve Effect of Scanning Beam Continuously Focused in Range" filed Aug. 5, 1983. In that system, the acoustic energy is projected upon the entire scene from different transducers in sequence, the reflected signals are processed so that those emanating from the same targets will additively combine in amplitude. Phase or time delay information in the echo signals is preserved and the resulting complex signals are vectorially added to produce an image comparable to that produced by a scanning beam which is continuously focused on all points in the scene.
The present system achieves some of the advantages of conventional large aperture systems, as well as achieving effective dynamic focusing on transmission, but also reduces the susceptibility of the system to motion of the body and reduces the time required to gather the data. Despite these advantages, however, the present system is considerably simpler than many conventional systems.
Accordingly, it is among the objects of the present invention to provide an ultrasonic imaging system which:
1. Is less susceptible to the effects of motion than other synthetic aperture systems. PA1 2. Does not require as long a time interval as other synthetic aperture systems to produce the data-representative signals required for display of an image. PA1 3. Approximates the use of a larger effective transmitting aperture. PA1 4. Enables the display of an image comparable to that resulting from employing a scanning beam of larger aperture which is continuously focused at all points on the scene, on transmission as well as reception. PA1 5. Improves the signal-to-noise ratio in the displayed image. PA1 6. Reduces and simplifies the required associated electronic hardware. PA1 7. Attains still other objects which will appear to one upon reading the specifications and claims and perusing the drawing herein.